CA1081426A

CA1081426A - Method of manufacturing fibreboard

Info

Publication number: CA1081426A
Application number: CA287,960A
Authority: CA
Inventors: Rolf B. Reinhall
Original assignee: Individual
Current assignee: Individual
Priority date: 1976-10-06
Filing date: 1977-10-03
Publication date: 1980-07-15
Also published as: DE2743652A1; FI67050B; FI772770A; NO773400L; FI67050C; JPS5391984A; BR7706650A; SE399015B; GB1587873A; US4311555A; FR2366928A1

Abstract

METHOD OF MANUFACTURING FIBREBOARD
ABSTRACT OF THE DISCLOSURE
Method of producing fibreboard products according to the so-called dry method from lignocellulosic fibre material in which the fibre material discharged from a defibrating apparatus in an en-vironment of steam is propelled in a stream of heated air to re -move substantially all moisture therefrom. The thus dried fibres are deposited on an underlying moving perforated screen to form a mat in which the fibres are oriented at random while propellant air is evacuated therefrom. The thus formed mat is wetted by add-ing water thereto while it is being advanced by the screen into a hot press where the wetted fibres are compressed and bonded in their random orientation, with consequent removal of water. The amount of water added in the wetting step is porportioned to be effective in itself to bond the fibres.

Description

BACKGROUND OF THE I~ENTION
Manufacturing fibreboard by the existing method involves us-ing the so-called wet method whereby the fibres are suspended in water which is then poured out on a screen so forming a sheet which is then given its final form in a hot press which also removes ex-cess water. One disadvantage with this formation method is that when the fibres in the water suspension are spread out over the screen, a process which occurs relatively rapidly, the fibres end up lying along the direction of the path of the machine, which 'j 25 results in a board in which the fibres are relatively oriented sub-stantially in one direction, This results in variations in strength lengthwise and crosswise of the sheet and in the board, which is disadvantageous.
In the production of boards according to the dry method, the sheet or mat is formed by suspending fine fibre particles in the air and depositing them on an underlying moving screen without any intermediate suspension in water. The so-called dry, half-dry of high-concentration forming methods result in a fibreboard in which the fibres are randomly oriented so that the sheet and t~e ~!
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10~426 final board are equally as strong in all directions. However, one disadvantage with this method is that size must be used to bind the fibres together, and this lengthens and complicates the pro-: cess.
SUMMARY OF THE INVENTION
In order to eliminate the disadvantages inherent in the fam-iliar methods described above, this invention contemplates a new high-concentration method for the manufacture of wet-pressed fibre-board which retains the advantages of the familiar methods, while eliminating their disadvantages. This method is particularly well suited for converting existing conventional factories using the wet method. A further object of the invention is to provide a complete-ly self-contained production process, thus eliminating the neces-sity of discharging waste and excess process water into lakes and ~; 15 watercourses.
These objects are realized according to this invention by wetting the layer of fibres once they have been deposited on the screen with a sufficient quantity of water so that it is essential-ly only the presence of the water in the final forming stage that gives the final board its necessary strength.
In terms of broad inclusion, the invention contemplates a mod-ification of the so-called dry method of producing fibreboard, in which the dry mat, prior to its advancement on the continuous screen into the conventional hot press, is wetted with an amount of water just sufficient to bond the fibres in their random orientation in the mat without the necessity of adding any extraneous adhesive or other bonding substances which are normally required in the conven-tional dry method of fibreboard production.
;~ Therefore, this invention retains the advantage afforded by ` 30 the dry method, namely, random orientation of the fibre, while, at the same time, the fibres are bonded by using water alone as the '~ bonding agent as in the wet method to impart to the final board the requisite strength. However, in contrast to the wet method, the

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10~314:~6 present invention provides strength and stability crosswise as well as lengthwise of the mat.
Furthermore, the forming technique taught by this invention may be combined with the conventional methods of manufacturing fibreboards in which the ligno-cellulose material is disintegrated at a temperature of at least 100C, and the energy supplied for the défibration and converted into steam generated in the process-ing of the fibres is separated and utilized to dry the fibres.
The dryness is thereby raised to a level equal to or in excess of that which is imparted to the fibre mat in the compression step -~
at the final stage of the process, before the heat which is sup-plied at this stage dries the fibre mat to its final dryness by driving off the moisture in the form of steam. ~-BRIEF DESCRIPTION OF THE DRAWING
The figure is a diagrammatic representation of a flow chart for a plant designed to perform the process according to the in-vention.
DETAILED DESCRIPTION OF AN EMBODIMENT OF THE INVEN~ION
In the practice of the invention, ligno-cellolose material, e.g., in the form of wood chips, is conveyed to a chip bin 10, from which a screw conveyor 12 or similar continually feeds the -material into a pre-heater 14 in which the chip material is heated to a temperature suitable for the process, usually in the range of 130C-170C, by steam supplied through a pipe 15. After pre-heat-ing, the material is conveyed by means of a feeding device 16 to a grinder 18 where the heated material is disintegrated into sep-arate fibres or clumps of fibres by grinding discs which rotate relative to one another. A motor 20 powers the grinder. The de-gree of fibre separation is adjusted according to the requirements set for the final product. The fibres separated by the grinding discs are conveyed from the grinding housing, which is at a pres-sure above atmospheric, via a discharge valve 22 and a so-called blow-off pipe 24, by steam generated during defibration or sup-.... . .
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- plied independently,to a receptacle 26. The receptacle 26 is de-signed in such a way that the fibres and the steam are separated by the combined effects of centrifugal force and gravity. The sep-arated steam is dispersed through an outlet pipe 28, either di-rectly into the atmosphere, or via a heat exchanger arrangement 30, so that the thermal energy in the steam can be recovered. This en-ergy can be used for purposes outside of the process described herein, but it can also be used to heat the air which is used to propel the separated fibres to the place where they are formed in-to a sheet or mat, as described below. The heat exchanger arrange-ment 30 is connected to a pre-heater or heat exchanger 38 by means of a pipe 32, a pump 34 and an expansion tank 36 for circulation of the heat exchanger medium, e.g., water, air or the like. Air drawn in by the fan 40 passes through the heat exchanger 38 as shown diagrammatically by the arrows. After having been heated in the pre-heater 38, the heated air is passed through a pipe 42 into the receptacle 26, where it entrains the fibres collected therein and propels them, by means of the fan 40 and the duct 42, to the mat forming station. The length of the duct is proportioned so as to allow for optimum utilization of the thermal energy transferred, through the pre-heating device 38 to the air, for drying the en-- trained fibres.
The duct 42 discharges into a dispenser 44 which is position-ed at the upper section of a pyramid-shaped cowling or hood 46 whose lower section is situated over a moving screen 48, which is preferably perforated and through which the air supplied by the - fan 49 via the dispenser 44 is evacuated into the atmosphere with the aid of a vacuum box 50 placed under the screen and a vacuum fan 52 connected to it. The fibres entrained in the steam are thus separated and are deposited on the moving screen 48, forming a layer of fibres against the discharge side of the forming device, the surface weight of the sheet or mat being adjusted so that it is equivalent to the surface weight of the final fibreboard re-,.
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1~814~6 sulting from the process. In order to produce a fibre mat of op-timum evenness, without use of an excessive amount of water, a planing device is positioned immediately after the point where the sheet emerges from the forming hood 46. The planed-away shav-ings are returned to the receptacle 26 or the dispenser 44 for ; re-use. By using the method as described and shown herein, thefibres are positioned at random on the moving screen, thereby im-i parting to the mat and the final product substantially uniform strength lengthwise and crosswise of the fibreboard.
Upon formation of the mat, it lea~es t~e ~ormation $tation, represented by the hood 46 - with or without planing - and it is then wetted or sprayed, e.g., through the nozzles 54, with the a-mount of water required to enable the fibre sheet to be compressed and/or dried sufficiently so that it will acquire essentially the same properties of strength and stability as fibreboards produced according to the conventional wet process without the use of size ;, or other extraneous bonding substances . The fibre sheet thereby , acquires a dryness of between 5% and 15%, which means that the fibre mat at this time, having been sprayed with water, will have a fiber content between 95% and 85%. It then passes through a conventional belt press 56 to compress the mat to the desired thickness, whereupon the mat, once it has been divided into sec-tions (not shown), is conveyed into a hot press where the mechan-ical compression into fibreboards takes place, with consequent , . . ..
;, 25 removal of excess water not required for the bonding of the fibres.
In the event the amount of water supplied by the nozzles 54 after the forming station 46 is such that the sheet's total water ~ content exceeds the amount of residual water in the boards at the i~ mechanical compression stage in the hot press 58, the water is '` 30 pressed out of the fibre sheet when it is compressed in the hot press 58 to form boards. This water, together with any water ~` which is extracted from the sheet when it passes through the press 56, if the amount of water applied was excessive, is drained into collection vessels 60, 62 and is piped to the subjacent water ~` A -5-4~6 ~anks 64 and 66, respectively. The water is pumped from the tank 64 via a pump 68 and a pipe 69 to the tank 66.
In certain cases, it may be required that the surfaces of the finished boards be coated with fibres of another material. These are supplied as shown diagrammatically at 72 from a storage place of the material to a tank 74 equipped with a mixer 73 where the ma-terial is suspended in water which can be supplied, e.g., via a branch pipe 76, from the tank 66, via a pump 78 and a pipe 79, to a so-called surface-coating box 81 of conventional type. The mater-ial in suspension, such as fibres, is thus deposited on the sur-face of the mat, while the water passes through the mat and the subjacent perforated screen in the normal manner. ~
A pipe 80 is provided for the supply of fresh water to, e.g., tanks 66 and 74 from a source (not shown), in order to maintain the necessary level of water in circulation and compensate for any pos-sible water losses.
In the embodiment shown, the surface-coating box 81 is po-sitioned between the hood 46 and the nozzles 54. Water is supplied to the latter from the tank 66 by a pump 70, through the additional branch pipe 77. Both the branch pipes 76 and 77 each have a regu-lating valve 88 and 90, respectively.
According to this invention, it is possible to return all the water recovered either to the surface-coating box 81, with or with-out the material in suspension, or to the nozzles 54. Possibly, one of the devices 81 or 54 may be dispensed with.
Water is removed in the form of steam when the board is com-pressed in the hot press, and this steam can be collected in a hood 82, and its thermal energy can be utilized as a heat exchanger med-ium in heat exchanger 84, prior to being discharged into the atmos-; 30 phere by a fan 86 or put to some other use. The heat exchanger 84 in the shown embodiment is connected to the heat exchanger coil of the receptacle 26 via the pipes 83, 85, but, naturally, the heat transferred can be used for other purposes if so desired.
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:1081426 It will be understood from the foregoing that this invention provides a process for manufacturing fibreboards which is similar to that used to manufacture the so-called wet fibreboards and which, from the point of view of quality and appearance, does not differ particularly from the conventional way of manufacturing fibreboards using the wet method with fibres suspended in water. However, the method of mat formation described herein produces a fibreboard with .
a greater Z-strength, because the fibres which make up the mat in this process are not uniformly positioned in one dominant direction and thus it completely eliminates the unavoidable variations in lengthwise and crosswise strengths which occur in fibreboards man-ufactured using the conventional wet method.
The method according to the invention eliminates the problem of pollution resulting from the discharge of the excess water lS pressed out of the mat formed according to the conventional wet method.

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Claims

THE EMBODIMENTS OF THE INVENTION FOR WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED, ARE DEFINED AS FOLLOWS:

1. The method of manufacturing fiberboard products according to the dry method from lignocellulosic moisture-containing fibers discharged from a defibrating apparatus, comprising the steps of:
a) propelling the fibers in a stream of heated air to re-move substantially all moisture therefrom;
b) depositing said dried fibers on an underlying moving screen to form a mat in which the fibers are oriented at random while removing propellant air therefrom with consequent inactiv-ation of the natural binders in the fibers;
c) wetting said mat by adding water thereto while advanc-ing it in its supported position on said screen without disturbing the random orientation of the fibers therein;
d) advancing said mat further on said screen into a hot press to compress the wetted fibers and bond them together in their random orientation with consequent removal of water;
e) the amount of water added at said wetting step being so proportioned as to reactivate the natural binders and be effective by itself to bond the fibers in the hot pressing step.

2. The method according to Claim 1, in which water is added in the wetting step in an amount to impart to the mat a dryness rang-ing between 5% and 15%.

3. The method according to Claim l, in which the heat quotient of the mechanical energy input during the defibration step is util-ized to heat the propellent air stream.

4. The method according to Claim 3, in which the heat quotient in the form of superatmospheric steam is separated from the fibers upon discharge from the defibrating apparatus and recycled in heat exchange with the propellent air stream.

5. The method according to Claim 4, in which steam generated in the hot pressing step is additionally recycled in heat exchange with propellent air stream.

6. The method according to Claim 1, in which water added in the wetting step in excess of that required for bonding the fibers in the hot pressing step is removed by compression of the mat prior to its advancement into the hot press.

7. The method according to Claim 6, in which free water re-moved in the hot pressing step is collected and recycled to the wetting step.

8. The method according to Claim 7, in which excess water is additionally collected and recycled to the wetting step.

9. The method according to Claim 8, in which a portion of the removed and collected water is utilized to produce a pulpable sus-pension of coating material for coating the dry mat.